Viscosities of n-Alkyl Chlorides from 15 to 80°C

The viscosities of n-alkyl chlorides from pentyl to hexadecyl chloride were determined at temperatures between 15 to 80°C at 5°C intervals. The intrinsic volumes of the n-alkyl chlorides were determined by extrapolation of the plot of fluidity against molar volume to zero fluidity. Plots of the logarithm of viscosity vs. reciprocal absolute temperature were almost linear. The energies of activation for viscous flow for the n-alkyl chlorides were calculated and found to increase with increase in chain length. The fluidities, , of the n-alkyl chlorides were found to obey the modified form of Hildebrand's equation. = D[(V-V_o/V_o]\exp(-E_B/RT) where D is a constant, V and V _o are the molar volume and the intrinsic molar volume, respectively, and E _B is an energy term corresponding to the energy required for disrupting the association of the molecules. The activation energy for viscous flow consists of the sum of the energy required for the expansion of the void volume and the energy required to overcome intermolecular interactions. These energies were calculated and discussed.     

Doxycycline Interferes with Zika Virus Serine Protease and Inhibits Virus Replication in Human Skin Fibroblasts

Zika virus (ZIKV) represents a re-emerging threat to global health due to its association with congenital birth defects. ZIKV NS2B-NS3 protease is crucial for virus replication by cleaving viral polyprotein at various junctions to release viral proteins and cause cytotoxic effects in ZIKV-infected cells. This study characterized the inhibitory effects of doxycycline against ZIKV NS2B-NS3 protease and viral replication in human skin cells. The in silico data showed that doxycycline binds to the active site of ZIKV protease at a low docking energy (−7.8 Kcal/mol) via four hydrogen bonds with the protease residues TYR1130, SER1135, GLY1151, and ASP83. Doxycycline efficiently inhibited viral NS2B-NS3 protease at average human temperature (37 °C) and human temperature with a high fever during virus infection (40 °C). Interestingly, doxycycline showed a higher inhibitory effect at 40 °C (IC50 = 5.3 µM) compared to 37 °C (9.9 µM). The virus replication was considerably reduced by increasing the concentration of doxycycline. An approximately 50% reduction in virus replication was observed at 20 µM of doxycycline. Treatment with 20 µM of doxycycline reduced the cytopathic effects (CPE), and the 40 µM of doxycycline almost eliminated the CPE of human skin cells. This study showed that doxycycline binds to the ZIKV protease and inhibits its catalytic activity at a low micro-molecular concentration range. Treatment of human skin fibroblast with doxycycline eliminated ZIKV infection and protected the cells against the cytopathic effects of the infection.     

Molecular dynamics simulation of monoalkyl glycoside micelles in aqueous solution: influence of carbohydrate headgroup stereochemistry

Comparative molecular dynamics simulations of n-octyl-beta-D-galactopyranoside (beta-C8Gal) and n-octyl-beta-D-glucopyranoside (beta-C8Glc) micelles in aqueous solution have been performed to explore the influence of carbohydrate stereochemistry on glycolipid properties at the atomic level. In particular, we explore the hypothesis that differences in T(m) and T(c) for beta-C8Gal and beta-C8Glc in lyotropic systems arise from a more extensive hydrogen bonding network between beta-C8Gal headgroups relative to beta-C8Glc, due to the axial 4-OH group in beta-C8Gal. Good agreement of the 13 ns micelle-water simulations with available experimental information is found. The micelles exhibit a similar shape, size, and degree of exposed alkyl chain surface area. We find net inter- and intra-headgroup hydrogen bonding is also similar for beta-C8Gal and beta-C8Glc, although n-octyl-beta-D-galactopyranoside micelles do exhibit a slightly greater degree of inter- and intra-headgroup hydrogen bonding. However, the main distinction in the calculated microscopic behavior of beta-C8Glc and beta-C8Gal micelles lies in solvent interactions, where beta-d-glucosyl headgroups are considerably more solvated (mainly at the equatorial O4 oxygen). These results agree with preceding theoretical and experimental studies of monosaccharides in aqueous solution. A number of long water residence times are found for solvent surrounding both micelle types, the largest of which are associated with surface protrusions involving headgroup clusters. Our simulations, therefore, predict differences in hydrogen bonding for the two headgroup stereochemistries, including a small difference in inter-headgroup interactions, which may contribute to the higher T(m) and T(c) values of beta-C8Gal surfactants relative to beta-C8Glc in lyotropic systems.     

Molecular design of liquid crystalline poly(ester-amide)s with perfluoroalkyl spacers

We have introduced a series of perfluoroalkyl dicarboxylic acids with different lengths of fluorinated aliphatic segments into the 2,6-acetoxynaphthoic acid (ANA) and acetoxy acetanilide (AAA) systems; and their effects on the evolution of liquid crystal texture and liquid crystallinity have been investigated. The perfluoroalkyl dicarboxylic acids are tetrafluorosuccinic acid (TFSA, n=2), hexafluoroglutaric acid (HFGA, n=3), perfluorosuberic acid (PFSUA, n=6) and perfluorosebacic acid (PFSEA, n=8). Computational results based on the 'RIS' Metropolis Monte Carlo method indicate that the ANA/AAA/perfluoroalkyl system may form thermotropic liquid crystalline polymers (LCPs) because the calculated persistence ratios are greater than 6.42. Computational results also predict that the systems containing even-numbered perfluoroalkyl acids have greater persistence length and molar stiffness than that containing odd-numbered acids. Experiments were carried out using the in situ thin film polymerization technique under a polarizing optical microscope. We observed that systems containing short aliphatic units (n=2, 3) tend to remain in the LC phase, while systems containing a long aliphatic spacer (n=8) tend to crystallize during the late stage of the polycondensation reaction. The liquid crystal domain formed in the early stage has a disclination strength S of +1. Ternary phase diagrams were plotted to show the relationship among monomer structure, composition, anisotropic and crystalline phases. FTIR results confirm the formation of LCPs.